45
It is 129.
28 (add on the prime number 11)
17
27.
27, 26, 37, 37
The answer of 17 + 123 is 140 and then minus 50 is 90
29
17
16 (add 3 every time).
5x + 17 = 7x - 123 123 + 17 = 7x - 5x 140 = 2x x = 140 ÷ 2 x = 70
The next number is 27. Nice puzzle! The reason is on discussion page, for those who are still working on it.
37 as each number is increasing by odd numbers like 3, 5, 7, 9